1. Field of the Invention
The present invention relates to a semiconductor module such as a multi-chip module.
2. Description of the Related Art
A DC-DC converter is a device that converts a certain voltage DC current into a different voltage DC current. The DC-DC converter is highly efficient and can be downsized. Therefore, it has been utilized as a power source incorporated in small electronic instruments (for example, information communications instruments such as notebook personal computers and mobile phones).
In the information communications instruments such as PCs, a CPU is fine patterned and sped up to provide an advanced low-voltage/large-current power source (drive power source). A supply voltage for the CPU is mainly 5.0 (V) or 3.3 (V) in the year 1995. In recent years, however, the debut of high-performance CPUs with clock frequencies over 1 GHz requires a voltage lowered down to 1.5 (V) and a current in a class of 100 (A). In addition, in order to respond to the operation speed of the CPU, the power source circuit is required to have an operation frequency of 1 MHz or higher. Therefore, it becomes also important to elevate the switching speed of transistors contained in the power source circuit.
The low-voltage/large-current power source has changed the forms of the conventional power source system. In a form of supplying power from a single power source to a plurality of circuits, even slight parasitic impedance on a wire causes a voltage drop. Accordingly, a voltage required for the circuit is not supplied, which causes erroneous operations. At present the form is therefore transferred to another in which power sources are distributed to locate the power sources corresponding to the respective loads close to the loads.
As for the notebook PC, for example, it comprises loads such as a CPU, a LCD screen and a hard disc. The power sources (that is, DC-DC converters) corresponding to the respective loads are located near the loads.
The conventional high-power DC-DC converters include a synchronous commutation non-insulating step-down converter, which comprises an N-channel type power MOSFET (Metal Oxide Semiconductor Field Effect Transistor), an SBD (Schottky Barrier Diode), a PWM (Pulse width Modulation) control IC and others. These components are individually packaged and the packaged components are mounted on a printed circuit board.
Normally, a power switching device such as the power MOSFET used in the power source circuit radiates heat caused from power losses due to on-resistance and switching. Therefore, it is required to attach a heat sink plate to the power MOSFET chip to dissipate the heat to outside the chip. A high-frequency multi-chip module structured to include a heat sink plate attached to a semiconductor chip is disclosed in JP-A 11-45976 (FIG. 1).